The MDS indicator LED is connected to one of the MDS solenoid circuits. When the solenoid is energized by the MDS system the LED comes on to indicate that the MDS has engaged.
I have a DIY write-up that I prepared for my 2005, with a parts list and pictures. Whether the wire color codes are the same in 2008 I don't know.
Drop me a PM with your e-mail address and I'll attach it with my reply.
2005 300C BRILLIANT BLACK, DRL, Mesh Grill/Vents, Chrome Pillars & Fender Trim, MDS Indicator, Quad Brake Lights, Tinted Windows, De-Molded, K&N Aircharger, 180 T-Stat, Flashing Sidemarkers, Predator Cust. Perf. 93 CAI Tune
1997 MUSTANG COBRA 'VERT, TRIPLE BLACK, Vortech S/C'd., ECT Mod., 4.10 Rear, 18" Saleen Wheels
1950 FORD TUDOR FLATHEAD V8, FLAT BLACK, 54 Chevy Grill, Nosed/Decked, Frenched Headlights, Air Shocks, Three-On-The-Floor w/OD, Dual Glasspack Exhaust, Dual Two-Barrel Carbs